1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a supercharger rotor.
2. Description of the Related Art
FIG. 1 is a schematic view of a supercharger rotor. The supercharger rotor comprises male rotor (M rotor 1) and female rotor (F rotor 2) rotated while being engaged with each other. The male rotor 1 includes a plurality (three in the drawing) of helical convex portions 1a, and the female rotor 2 includes helical concave portions 2a engaged with the helical convex portions 1a with no gap. Gas (e.g., air) is compressed between the helical convex and concave portions 1a and 2a, and the air is pressurized to supercharge in an internal combustion engine.
The supercharger rotor also comprises a profile portion 3 having the helical portions 1a and 2a, and a shaft 4 penetrating the profile portion 3. The profile portion 3 is normally made of aluminum, and the shaft 4 of steel. Accordingly, in order to firmly connect the profile portion 3 with the shaft 4, conventionally, metal bonding means has been employed to execute aluminizing for the shaft side, and connecting the shaft made of steel with the profile portion made of aluminum. In this case, since the shaft 4 and the profile portion 3 are connected with each other by metal bonding, the rotor must be maintained at a high temperature for a long time.
Conventionally, the supercharger has been manufactured by gravity casting or precision casting.
The gravity casting is a method of manufacturing a rotor by pouring molten metal (hot metal) into a mold, and solidifying it. For the mold, a sand mold or a metal mold is most often used. The mold has a cavity portion equivalent to a product (rotor in this case), and hot metal can be poured into this portion.
For the gravity casting, in the case of mass production, automization has been pursued in various manners. Still, however, manufacturing of a die or its disassembling takes time (e.g., about 6 min.), lowering productivity. Since feeder head twice as much as a product is necessary, lowering yield, and increasing costs. Because of low accuracy of a casting, an excess thickness of about 3 mm is necessary, accordingly increasing a processing margin, which result in longer processing time, and higher processing costs. Further, it is difficult to provide a helical hollow portion inside the rotor having the helical portion, consequently making the rotor heavy. Thus, the conventional rotor has many drawbacks such as a large moment of inertia, unsuitable for high-speed rotation and operation stop characteristics, and low response to an engine speed.
On the other hand, the precision casting is a shell mold method or a lost wax method, and characterized by high accuracy of a casting. However, it is substantially impossible to manufacture a rotor by the shell mold method. In addition the lost wax method includes many steps, lowering productivity, and increasing costs. Further, although the helical portion can be made hollow or the shaft can be cast-coated, costs are higher.
In order to solve the above-described connection problem by the aluminizing, means has been provided to fix a profile portion and a shaft to each other by a pin, or provide a groove 5 in a shaft 4, and cast-coat it as shown in FIG. 2A (Japanese Patent Application Laid-Open No. 301211/1995), or means has been presented to provide a through-hole 6 in a shaft 4, and cast-coat it (Japanese Patent Application No. 49677/1996). In these means, however, problems of high costs caused by increases in processing steps and components have been inherent.
The present invention was made to solve the foregoing problems. Specifically, a first object of the present invention is to provide a method and an apparatus for manufacturing a supercharger rotor, which is capable of inexpensively and efficiently manufacturing a rotor for a supercharger, reducing costs by greatly reducing a processing margin, and enhancing high-speed rotation and operation stop characteristics, and response to an engine speed by greatly reducing weight. A second object of the present invention is to provide a method for manufacturing a supercharger rotor, which is capable of inexpensively, efficiently and firmly connecting a profile portion and a shaft, constituting the supercharger rotor, with each other.
In order to achieve the first object, in accordance with the present invention, there is provided a method for manufacturing a supercharger rotor, a plurality of profile portion divided metal molds (12) surrounding a profile portion (11a) of a supercharger rotor (11) to allow division, and a pair of end metal molds (14, 15) surrounding both ends (11b) of the rotor being provided, and a helical core (16) helically passed through the profile portion of the rotor being attached to one end metal mold (14), the method comprising the steps of: (A) forming a rotor-shaped cavity (13) inside by the profile portion divided metal molds and the end metal molds; (B) pressurizing hot metal, and injecting and solidifying the hot metal in the cavity; and (C) pulling out the end metal mold (14) having a helical core by rotating the same along a helical line.
In accordance with the present invention, there is provided an apparatus for manufacturing a supercharger rotor, comprising: a plurality of profile portion divided metal molds (12) surrounding a profile portion (11a) of a supercharger rotor (11) to allow division; a pair of end metal molds (14, 15) surrounding both ends of the rotor; a helical core (16) attached to one end metal mold (14) to be helically passed through the profile portion of the rotor; and a rotary pulling-out device (18) for pulling out the end metal mold (14) having the helical core by rotating the same along a helical line.
According to the method and the apparatus of the present invention, by die-casting for forming the rotor-shaped cavity (13) inside with the metal molds (12, 14 and 15), and pressuring hot metal (e.g., aluminum), and injecting and solidifying the hot metal in the cavity, it is possible to manufacture a supercharger rotor inexpensively and efficiently.
By attaching the helical core (16) to one end metal mold (14) so as to be helically passed through the profile portion of the rotor, and pulling the end metal mold (14) by rotating the same along a helical line, the rotor can be made hollow. Thus, the hollow shape enables the rotor to be made thin, casting defect inherent in die-casting to be prevented, weight to be greatly reduced, and a moment of inertia to be reduced. As a result, it is possible to enhance high-speed rotation and operation stop characteristics, and response to the engine.
Furthermore, compared with gravity casting, in die-casting, there are no feeder heads, and accuracy is high. Thus, it is possible to reduce processing costs by making an extra thickness small (e.g., about 0.5 mm), and greatly reducing a processing margin.
According to a preferred embodiment of the present invention, for the helical core (16), sectional shapes orthogonal to a rotor shaft are similar, and an attached portion to the end metal mold (14) is formed thick, and gradually made thinner toward a tip.
With such a constitution, when the rotary pulling-out device (18) pulls out the end metal mold (14) by rotating the same along the helical line, a casting rotor and the helical core (16) can be smoothly separated from each other (mold releasing), increasing die-casting productivity.
In order to achieve the second object, in accordance with the present invention, there is provided a method for manufacturing a supercharger rotor by casting a profile portion (21a) of a supercharger rotor (21) and a shaft (22) penetrating the same, comprising the steps of: (D) first processing a left and right helical cross portion (23) on a surface of the shaft connected to the profile portion; and (E) casting the profile portion (21a) around the shaft in die-casting.
According to a preferred embodiment of the present invention, the left and right helical cross portion (23) includes a right handed screw helical groove, and a left handed screw helical groove, and these grooves are caused to cross each other.
According to the method of the present invention, by forming a groove in the shaft, when casting is executed in die-casting, aluminum is surely injected by a casting pressure into the cross groove portion (23) formed on the surface of the shaft 22, and a sufficient fastening force is provided by mechanical connection.
Therefore, the conventional aluminizing to the shaft side is made unnecessary, and groove formation and penetrating are also made unnecessary. The number of processing steps is accordingly reduced, and extra components are made unnecessary. As a result, it is possible to firmly connect the profile portion and the shaft with each other inexpensively and efficiently.
Other objects and advantageous features of the present invention will become apparent by the following description made with reference to the accompanying drawings.